Insulated electric conductor



Oct.- 4, 1938; R. D. QGR'EIEN Y 2,132,235

INSULATED swarms conwcwon Filed llarch 1s, i954 INVENT'OR BY I ATTORNEYSPatented Oct. 4, 1938 UNITED STATES PATENT OFFICE 2,132,235 INSULATEDELECTRIC CONDUCTOR Application March 13, 1934, Serial No. 715,268

2 Claims.

This invention relates to an insulated electric conductor.

It is common in the art to provide an insulated stranded conductor forfield telegraph work, Q such as signal service work, where the conductormust be capable of withstanding considerable mechanical abuse when beinghandled, particularly when being laid on or taken up from the ground,and must be well insulated so that even 10 if laid on damp or wetground, it will perform satisfactorily as an electric conductive pair;also it must be flexible enough to be reeled up and unreeled repeatedlyand so light in weight that long lengths may be carried readily fromplace ll to place, for example, by one man.

The insulated conductors of this kind are generally provided with atleast two relatively small wires of good conductive non-ferrous metal,

stranded with steel wires. However, it has been 20 found that theinsulated conductors hitherto known are not only difllcult tomanufacture but are not durable for the reason that, due to the frequentbending of the wires of the stranded conductors, as for example, inhandling it in the 26 field, the insulation is destroyed or seriouslyinjured largely by the so-called creeping of some of the wires relativeto the insulating coating, this creeping" being a slight longitudinalshifting of a wire or wires in the strand, not neces- 30 sarilythroughout the entire length of the conductors, but only locally,involving sometimes a drawing or stretching of such creeping wire orwires and a. consequent reduction in the crosssection of such wire orwires, which often re- 35 suits in a broken wire or wires and injuresthe insulation, so that the conductors are grounded or short clrcuited.As a result it has sometimes been considered advisable to employ wiresof slightly larger gage than would be necessary 40 otherwise forconduction of the telegraph currents, to'allOw for the slight drawingaction due to creeping,'and thereby give the conductor a longer usefullife. The result of this use of a heavier gage size of wire, of course,increases the weight of the conductor and thereby reduces its convenientportability.

It is the object of the present invention to overcome the difficultiesdue to the said creeping 50 action in conductors of this kind and toprovide a more durable yet light, insulated stranded conductor, whichwill be sufilciently flexible to meet all requirements, but not soflexible as to, kink easily.

55 With these general objects in view the invention consists in thehereinafter described and claimed conductor.

The invention will be described in detail in connection with theaccompanying drawing, in which 5 Fig. 1 is aperspec tive view on a verylarge scale intended to illustrate a short length of conductor embodyingthe invention, with parts re-- moved.

Fig. 2 is a cross-section on an enlarged scale, of the conductorillustrated in Fig. 1.

Fig. 3 is a diagrammatic view illustrating the principle of theinvention, and shows how the integral series of metallic coatings forthe wires,

"would appear at a particular cross-section, if the wires could beremoved from the metal coatings.

In flexible insulated conductors used for field telegraph work it isimportant that the completed conductor be so well insulated that it maybe laid along the ground, ifnecessary, and will not permit anyappreciable leakage of current. Also, it must be so flexible that it maybe reeled up readily and unreeled, and should be so durable that it willwithstand many repetitions of such treatment without breaking.Furthermore, in order to 'meet the requirements of practice it must berelatively light for its conductivity so that considerable lengths maybe transported readily.

In order to obtain this ready portability, the total cross-section ofall the wires must be kept to a minimum for the requisite conductivityand strength. This results in the individual wires being quite small indiameter.

Since it is necessary to use vulcanized rubber for the insulatingcoating, the sulphur of the vulcanizing compound is likely to corrodethe wires, particularly copper wires, and although in practice the depthof the outer layer of the wire corroded by the reaction of thevulcanizing material is extremely small, it is a material proportion ofsuch a fine wire and the loss of conductivity and breaking of wires dueto corrosion fatigue thereby resulting, is important. Hence, to protectthe wires against this corrosion due to the reaction of the vulcanizingmaterial it is necessary to give the wires a coating of some metalresistant to such corrosion. The recognized protective coating for thispurpose is a tin coating, although other corrosion-resistant low-meltingmetals may be used, such metal being applied in a molten condition andthen set by cooling. With a perfect tin or other metal coating the wireis fully protected.

However, it is extremely expensive and dimcult to apply aperfectlyuniform and adequate coating to the wire at all points. This isparticularly true with small wires. Hence, it has been the practice torun the wire very slowly through the molten metal bath in order toobtain the required thickness of coating. Owing to the fineness of thewires; the difiiculties in handling the wires through the pickling andfluxing baths and particularly through the baths of molten metal areconsiderable, as is well known to those skilled in the art.

As the copper wires must be stranded with steel wires, in order toobtain the requisite strength in the final stranded composite conductor,it is important that the individual steel wires also be given aprotective coating, particularly to protect them against rusting. Withtinned copper, bronze or other non-ferrous or alloy wires, the steelwires also are tinned or coated with other protective metal, and it isnecessary to run the wires very slowly through the molten metal bath forthe same reason stated above with regard to the copper wires.

By the present invention all the difliculties of manufacture abovereferred to are avoided and a better conductor produced bystranding thebare wires, or at most merely applying one thin coating of tin, or othermetalat very high speed,

. to each wire and then stranding them, and theretective metal, on steeland copper, the great surface tension, and the resultant capillaryaction, the molten metal is drawn'in, even between the contacting wiresso as to coat all parts of the surface of the wires. Also the individualwires are locked together preventing any creeping of the individualwires in the strand and consequent injury to the insulating coveringsuch as occurs in practice with the insulated conductors made byapplying the usual coating of tin to each wire separately, thenstranding the coated wires and applying the rubber coating andvulcanizing it.

' Practice has shown that the molten tin is taken up with such avidityby the stranded conductor that even with only one pass through themolten bath, the stranded conductor takes up and holds several times theamount of tin, or other protective coating, carried by the old strandedconductor of the prior art where the individual wires have been passedthrough the bath of molten metal.

After the stranded conductor has been tinned, or coated with othermetal, the vulcanizable rubber composition, or other insulatingmaterial, is applied in the usual manner and proportions and thenvulcanized or treated by heat, or other medium.

A field telegraph conductor embodying one form'of the invention isillustrated in Fig. 1, but on a greatly enlarged scale, this conductorconsisting of three hard drawn copper wires, of high specificconductivity indicated at I and four steel wires 2 of metal having ahigh coemcient of elasticity and high tensile strength, these wiresbeing all of approximately the same diameter and advantageously arrangedas shown, that is, with the three copper wires in a line and the foursteel wires in pairs, one pair at each side of the line or tier ofcopper wires. In practice, for fl'eld telegraph work, each wire is about0.0126 in diameter, that is, about #28 B. & S. gage. With the properselection of materials, the copper wires will give about of theelectrical conductivity of the completed conductor and the four steelwires about 10%. The four steel wires will provide about 90% of thetotal tensile strength of the strand and the three copper wires about10% ofthe said total tensile strength.

In the best embodiment of the invention the individual wires beforebeing united into a strand may be given a single light coat oflow-melting metal, such as tin,-not for the purpose of protecting thewires, which is impossible with a light single coating, on account ofits certain defectiveness, but as a means for slightly spacingthewiresapart in. the strand with a relatively easily fusible materialwhich will become molten when the entire strand is passed into a moltenbath of the same material, as more fully described hereinafter. However,I have discovered that this light spacing coating is not unconditionallynecessary, particularly if the wires be not tensioned too much duringthe stranding operation, but are slightly loose in the strand.

After the light coating of the individual wires has been applied, andthey are brought together in a strand, or after the clean bare wires arebrought together somewhat loosely in a strand, the completed strand isthen passed through suitable cleaning and fluxing baths, if necessary,and then is drawn through a bath of molten tin, or other protectivemetal, at such a rate that the strand will take up a heavy coat of theprotective metal, the strand being in the molten metallong enough tomelt the light spacing coating if that has been used, and long enoughfor the capillary action or surface tension of the a molten metal todraw it down into the spaces between the individual wires as well asover all the surfaces of said wires,- so that finally the molten metalwhen set forms a single integral body, about as shown on an exaggeratedscale in Fig. 8, consisting of a plurality of coatings for theindividual wiresunited to each other at the places of contact of suchcoatings, these places being the spaces between the wires. The conjointintegral coating system is indicated at 3 in the drawing.

It has been found that by this method of procedure about five or sixtimes as much metal can be applied to the strand as will be the case ifthe individual wires are properly coatedbefore stranding by the old andvery expensive method.

Furthermore, as the strand formed of a plurality of wires is muchstronger, of course, than any individual wire, there is no difiiculty inpulling it through the bath of molten metal and because'a strand is notso-extremely flexible as a single wire, and particularly a 'copper.wire, all the dangers of kinking and breaking whichexist with theindividual wires in individually applying a coat of metal on the wiresseparately, are avoided.

Of course, where the individual wires are given the light spacing coatof metal before stranding, some of the difliculty still exists, but asno reliance is placed on this light coating for the final protection ofthe wire and asthe wire is not so heavily-loaded with protective metal,it-need not be strained to the same extent during coating, and inanyevent the difiiculty encountered in applying the coating by the priormethod is entirely avoided.

. When the strand is passed once through the bath of molten metal andhas been cooled, it will be found that the wires are locked together, sothat the individual copper wires are secured firmly to their adjacentsteel wires and hence cannot creep at any part.

Upon this coated stranded plurality of wires there is applied a mass 01'rubber compound containing the materials for vulcanization, this coatingbeing applied to the stranded wires in any of the known ways, as forexample, by extruding the rubber compound around the strand in the usualmachine or by passing strand through liquid rubber. The coating is shownat 4, Figs. 1 and 2.

Then the strand with its coating of insulating material is subjected toheat to vulcaniz'e the insulating coating.

It will be noted that the tin, or other protective metal coating, onaccount of its increased amount somewhat reduces the flexibility or theconductor as compared with the flexibility oi the conductor made by theprior methods, but that is an advantage, because it avoids the danger ofsmall loops which result in kinks in the field, a danger which existedwith the prior field telegraph conductors due to their unnecessarilygreat flexibility. At the same time, the conductor of the presentinvention has all the necessary flexibility for ease and convenience inreeling and unreeling, and in shifting its position on the ground whennecessary. Furthermore, in view of the possibility of using wires of thesmallest gage necessary to supply the requisite conductivity, ductor ofthis invention is no greater than that oi a conductor made by the oldmethod using a slightly heavier gage for mechanical reasons inmanufacture.

the final weight per foot oi the con- While in the present example, Ihave shown three copper wires and four steel wires in the conductor, theinvention is not to be limited to this exact number of wires.

The legends on the drawing are added by way 01' illustration and not byway of limitation.

What is claimed is:

1'. An insulated stranded conductor consisting ofa plurality of wiressome of which are copper of high conductivity and the remainder steel ofhigh elastic limit and high tensile strength, each of said wires beingcoated with low-melting protective metal having the properties of metalset from a molten state, said protective coatings being integral witheach other at their respective places of contact and firmly connectedwith each other by an integral mass of metal filling the interspacesbetween the inner portions of the respective surfaces of the wires,whereby creeping oi the individual wires is prevented, the unitedstranded wires being embedded in vulcanized rubber which forms aninsulating coating surrounding the stranded wires.

2. A field telegraph conductor consisting of a plurality of copper wiresand a plurality of steel wires of high elastic limit and tensilestrength, said wires being of small diameter and stranded together, eachof said wires being completely tin coated, all of the tin coatings beingintegral with each other at their respective places of contact. wherebycreeping of the individual wires is prevented, the united stranded wiresbeing embedded in a sheath of vulcanized rubber which forms aninsulating coating surrounding the stranded wires.

RICHARD DUANE GREEN.

